This renewal application for the next four years develops from our interest in structure-function relationships in gut endocrinology. 1) The first overall objective will be the elucidation of molecular events controlling the secretion of hydrolases from pancreatic acinar cells. The interactions between gastrointestinal hormones (and "candidate hormones"), specific receptors, and effector units, including the role of GTP in the adenylate cyclase system, of phosphatidylinositol turnover, and of the calcium-dependent activator of cyclic GMP phosphodiesterase will be investigated. Radiolabelled ligands such as (3H) Gpp(NH)p, (3H) bombesin, (125I) bovine pancreatic peptide and (3H) muscarinic antagonist will be used, in addition to (125I) VIP and (3H) caerulein. Quantitative correlations between physiological effects, spare receptors, classes of binding sites and negative cooperativity will be established. The turnover of hormone receptors and their purification will represent two other major goals. This interest in the exocrine pancreas will be extended to more plasma membrane activities (Ca2 ion-Mg2 ion-ATPase and protein phosphorylation); to the intermediary metabolism of the gland, and to the molecular biology of centroacinar and duct cells. 2) Using the pancreas as a target tool, we wish to identify the presence in gut and brain of (prepro) hormones and hormone fragments of the pancreozymin family. This will be accompanied by a study of their biosynthesis. 3) Apart from a number of chromatography procedures, our array of specific methods includes dispersed pancreatic cells, purified plasma membranes, radioactive ligands, calcium transport, and cyclic AMP and cyclic GMP determinations.